| 摘要 |
PROBLEM TO BE SOLVED: To control the output characteristic of a light beam by setting the structure of a 1st surface as the form of plural triangular prisms, making the respective prisms have an apex angle and making some of the apex angles different from others. SOLUTION: The film 16 has a 1st principal surface (front surface) 18 and a 2nd principal surface (front surface) 20. The surface 18 has plural prisms acting as a light beam extracting device, and, on the other hand, the surface 20 has a Fresnel lens forming an output light beam. Then, plural triangular prisms are positioned on the side 18 of film 16. Namely, the surface 18 has the structure of the form of plural triangular prisms, and the respective prisms have the apex angle, and some of the apex angles are made different from others. In such a case, it is desirable to use the prism of isosceles triangle shape as the prism, because the prism acts equivalently to the light beam from any direction. Therefore, an illumination tool performs irradiation at both ends and more light beams and uniformity are obtained. |
